If you plan on playing Terraria with some friends, you may be hoping to host a server on your PC for everyone to play on. As a little tip, the best person to host the server is the person with the best PC, and who is closest to everyone else in the group to ensure everyone has the best possible connection.
For the most part, this is as simple as going into Multiplayer, then clicking on the option to Host. However, You will need to know your IP as your friends will need to connect directly to the IP address.
To find out what your IP address, you can use a website like WhatsMyIp. The site will tell you your IP address at the top, and you can then give it to your friends.
Hosting a Terraria server can be a surprisingly complex, or incredibly easy, it depends on how deep you want to get into things. Hosting it on your PC is a great option, but remember that your friends will only be able to play while your PC is turned on. You can, if you wish, set up a dedicated server.
For a full walkthrough on the details you need to host a server, we suggest you check out this article on the Terraria Gamepedia. They have a complete and very detailed write up on everything you need to know to host your own Terraria server, especially if you want to get into complicated areas like configuration files.